In my parent application there was provided a method and apparatus to improve the recovery of fuel burning power generators and the like while minimizing emissions of sulfur and nitrogen to the atmosphere.
In the process as described, after combustion of a carbonaceous fuel such as coal, there is introduced a secondary hydrocarbon, such as methane, capable of forming a reducing gas into the combustion chamber to scavenge excess oxygen and create reducing atmosphere for the subsequent reduction of the oxides of sulfur to hydrogen sulfide and the oxides of nitrogen to inert nitrogen and/or ammonia with nitrogen formation being favored.
The gas stream is then allowed to pass through the remaining sections of the boiler and to an added catalytic conversion zone containing a catalyst capable of converting the oxides of sulfur to hydrogen sulfide by reaction with the hydrogen present in the reducing gas and the oxides of nitrogen by reaction with the reactants present to form inert nitrogen and/or ammonia at a temperature from about 300.degree. to about 800.degree. F.
Many other operations exist where there is a requirement for a reducing gas comprising hydrogen and/or carbon monoxide reductants, such as for regeneration of SO.sub.2 absorbants, and reducing in external streams the oxides of sulfur and nitrogen. Usually such reducing gases prepared by reacting steam plus hydrocarbons at high temperatures (1200.degree.-1800.degree. F) over a catalyst. The principal chemical reactions which take place using methane as a typical hydrocarbon are: EQU CH.sub.4 + H.sub.2 0 .fwdarw. CO + 3H.sub.2 ( 1) EQU co + h.sub.2 o .fwdarw. co.sub.2 + h.sub.2 ( 2)
another method is to burn a hydrocarbon with substoichiometric air at elevated temperatures (2000.degree.-3700.degree. F). The principal chemical reactions taking place in this process are: EQU CH.sub.4 + 1/2O.sub.2 .fwdarw. CO + 2H.sub.2 ( 3) EQU ch.sub.4 + 2o.sub.2 .fwdarw. co.sub.2 + 2h.sub.2 o (4)
In both cases a relatively expensive hydrocarbon fuel must be used as the sole fuel and/or as the process material. In the commercial application via the steam methane reforming of (1) and (2) above, a fairly expensive furnace must be employed with high-alloy tubes to contain the catalyst and to withstand high furnace temperatures. The cost of such equipment is becoming prohibitively expensive.